An international team of astronomers has discovered a pulsar — the core of a massive star that exploded as a supernova — spinning at more than 42,000 revolutions per minute, making it the second-fastest known.
PSR J0952-0607 (lower right) rotates 707 times a second and now ranks as second-fastest pulsar known. The location of LOFAR’s first millisecond pulsar discovery, PSR J1552+5437, which spins 412 times a second, is shown at upper left. Image credit: NASA / DOE / Fermi LAT Collaboration / ASTRON.
The object in question, dubbed PSR J0952-0607 is a so-called millisecond pulsar. It is located between 3,200 and 5,700 light-years away in the constellation Sextans. It contains about 1.4 times the Sun’s mass and is in a 6.42 hr orbit around a very low-mass companion (less than 20 times the mass of Jupiter).
At some point in PSR J0952-0607’s history, matter began streaming from the companion and onto the pulsar, gradually raising its spin to 707 rotations a second (more than 42,000 rpm) and greatly increasing its emissions. Eventually, the pulsar began evaporating its companion, and this process continues today.
Because of their similarity to spiders that consume their mates, systems like this one are called ‘black widow’ or ‘redback’ pulsars, depending on how much of the companion star remains.
PSR J0952-0607 was spotted the Low Frequency Array (LOFAR) radio telescope in the Netherlands, and is described this week in a paper published in the Astrophysical Journal Letters.
“The LOFAR discovery also hints at the potential to find a new population of ultra-fast pulsars,” said lead author Dr. Cees Bassa, of the Netherlands Institute for Radio Astronomy.
“LOFAR picked up pulses from PSR J0952-0607 at radio frequencies around 135 MHz, which is about 45 percent lower than the lowest frequencies of conventional radio searches.”
“We found that PSR J0952-0607 has a steep radio spectrum, which means its radio pulses fade out very quickly at higher frequencies. It would have been a challenge to find it without LOFAR.”
Astronomers say pulsars could rotate as fast as 72,000 rpm before breaking apart, yet the fastest spin known — by PSR J1748–2446ad, reaching nearly 43,000 rpm — is just 60% of the theoretical maximum.
Perhaps pulsars with faster periods simply can’t form. But the gap between theory and observation may also result from the difficulty in detecting the fastest rotators.
“There is growing evidence that the fastest-spinning pulsars tend to have the steepest spectra,” said co-author Ziggy Pleunis, a doctoral student at McGill University.
“The first millisecond pulsar discovered with LOFAR is PSR J1552+5437, which spins at 25,000 rpm and also exhibits a steep spectrum.”
“Since LOFAR searches are more sensitive to these steep-spectrum radio pulsars, we may find that even faster pulsars do, in fact, exist and have been missed by surveys at higher frequencies.”
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C.G. Bassa et al. 2017. LOFAR Discovery of the Fastest-spinning Millisecond Pulsar in the Galactic Field. ApJL 846, L20; doi: 10.3847/2041-8213/aa8400
